Phivolcs: Expect more aftershocks after Visayas quake

By Caroline J. Howard, ANC

Posted at Feb 08 2012 04:49 PM | Updated as of Feb 09 2012 12:58 AM

MANILA, Philippines -- Frequent seismic activity will continue to be felt for several days after a magnitude-6.9 earthquake struck Negros province on Monday.

More than 1,200 aftershocks have been recorded. But the Philippine Institute of Volcanology and Seismology (Phivolcs) described this situation as "normal" for a magnitude-6.9 quake.
"There will always be aftershocks after a big activity. We expect a lot of earthquakes as part of the adjustment being done because the rupture zone extends 50 to 80 kilometers. That means it has moved. Some areas are compressed, others dilated. That means those areas are adjusting. Until such time it has stabilized, the earthquakes won't stop," Ishmael Narag, officer in charge of Phivolcs' seismology division, said on ANC's "Headstart" on Wednesday.

"A lot of those epicenters are lining up along the rupture zone. At least we've already identified where the fault trace should be," he said.

According to Phivolcs, an active but previously unmapped fault along the stretch of Negros generated Monday's earthquake.

Narag admitted that the agency's efforts in identifying faultlines are weighed down by the lack of high-resolution topographic maps and the lack of experts skilled at active faults mapping.

"The fault is covered by so much sediments that features that we find in a low-resolution map is not that visible," he explained. "What we need are high-resolution topographic maps to identify any features on the surface that would indicate past rupturing...We couldn't find an active fault responsible for this earthquake so we decided it's possibly a lining across coast of Negros."

Narag added that the agency is also being hampered with the departure of geologists for more attractive career opportunities.

"Specialists with training on active faults mapping are pirated by mining firms. You cannot blame them.  That's where the money is right now," he said.

But Narag stressed that hazard-mapping is being done except that the priority is on densely populated areas.

"There are priority areas. We prioritize areas that are densely populated like Metro Manila, Davao, Cebu, which are at high risk of earthquakes. As such we need to pull resources that way," he said.

Need for faultline markers

World-class architect and urban planner Jun Palafox noted that sophisticated base maps are done by other government agencies, not by Phivolcs.

Phivolcs has been doing the prioritization of hazard areas together with the Philippine Atmospheric, Geophysical, and Astronomical Services and the Mines and Geosciences Bureau. National Mapping and Resource Information Authority is the mapping agency providing the base maps for Phivolcs.

Aside from hazard-mapping and the structural audit of buildings, Palafox, the founder of Palafox Associates, said the government should also assign evacuation areas as part of its zoning efforts for immediate use in case calamity strikes.

Palafox also advised the government to put up monuments near faultlines as a warning to the public.

"I think they should already put monuments near the faultlines. In California (where the world-famous San Andreas fault is located), it's even a tourist attraction.... How come Philvocs or the government don't put monuments to mark where the faultline is?" he asked.

 Narag, however, explained Phivolcs had tried putting up markers in areas near faultlines but the plan was short-lived.

"We partnered with Quezon City and placed markers on areas near faultline. After a week, they took it out. People are not that receptive if their areas are transected by faults," he said.

According to Palafox, former Phivolcs director Raymundo Punongbayan had wanted to publish where the country's faultlines lie. "He told me he was pressed by vested interest groups because their land values might go down," Palafox said.

Palafox and Narag agreed that government should work closely with scientists and urban planners in producing more helpful maps.

They also stressed the need for the enactment of more laws that will raise safety standards in areas that are vulnerable to earthquakes.

Metro Manila study

In 2004, a study by Japan International Cooperation Agency (JICA) together with Phivolcs showed that 40% of low-rise structures in Metro Manila would collapse in the event a magnitude-7.2 earthquake struck the metropolis because they were either not properly designed, not built on stable ground or were built on top of a faultline. 

Citing the same study, Palafox said the quake would result in the death of 32,000 people, with 18,000 more killed in an ensuing fire.

He added that Metro Manila would be divided into four quadrants: east and west of the faultline and north and south of the Pasig River because some bridges might fall and utility services will be cut.

The JICA study showed high-rise structures would fare better because they also complied with a performance-base code that follows best practices in Chile, California, Japan and Taiwan -- areas that are prone to earthquakes.

Palafox said the government should update its land use, zoning and building codes, identify sites for proposed evacuation, and ensure infrastructure and homes are structurally sound, built to better withstand earthquakes, and only in areas deemed safe.

"Unfortunately, despite so many development and building permits, houses and structures were built above that faultline. You should never build on top of a faultline. You can build five meters away from it, but some buildings were allowed to be built on top of it. I think immediately now, houses and structures on top of faultlines should be relocated or removed right away," he said.